1. Field of the Invention
The present invention relates to an on-vehicle electronic controller incorporating a microprocessor used for controlling fuel supply of a vehicle engine and so on. The invention particularly relates to an on-vehicle electronic controller that is improved in handling a large number of input/output signals and in standardizing the controller regarding the control on various types of vehicles.
2. Description of the Related Art
FIG. 9 is a typical general block circuit diagram showing one of conventional on-vehicle electronic controllers of this type. An ECU (engine control unit) 1 comprised of a single printed circuit board includes a LSI (integrated circuit) 2 as a main component. In the LSI 2, a CPU (microprocessor) 3, a nonvolatile flash memory 4, a RAM memory 5, an input data selector 6, an A/D converter 7, an output latch memory 8 and so on are connected via a data bus 30. The ECU 1 operates in response to a control power supplied from a power supply unit 9, which is fed from an on-vehicle battery 10 via a power supply line 11 and a power switch 12. An execution program, a control constant for controlling an engine, and so on are stored in the nonvolatile flash memory 4 in advance.
Meanwhile, a large number of ON/OFF input signals from various sensor switches 13 are supplied from a bleeder resistors 14 serving as a pull-up or pull-down resistance, to comparators 19 via series resistors 15 and parallel capacitors 16 that constitutes a noise filter. Input resistors 17 and reaction resistors 18 are connected to the comparator 19. When a voltage across the parallel capacitors 16 exceeds a reference voltage applied to a negative terminal of the comparator 19, a signal of logic xe2x80x98Hxe2x80x99 is supplied to the data selector 6. However, when decreasing the voltage across the parallel capacitors 16, the input from the reaction resistor 18 is added thereto. Therefore, the output of the comparator 19 returns to logic xe2x80x98Lxe2x80x99 since the voltage further decreases to less than the reference voltage. As described above, the comparator 19 acts as a level judging comparator including a hysteresis function, and a large number of outputs from the comparators 19 are stored in the RAM memory 5 via the data selector 6 and the data bus 30.
In addition, for example, the mentioned data selector 6 handles an input of 16 bits and outputs the input to the data bus 30 when receiving a chip select signal from the CPU 3. Input points range over several tens points, and a plurality of data selectors are used.
Further, a large number of analog signals from various analog sensors 20 are supplied to the A/D converter 7 via series resistors 21 and parallel capacitors 22 that constitute a noise filter. Digital outputs from the A/D converter that receive chip select signals from the CPU 3 are stored in the RAM memory 5 via the data bus 30. Control outputs from the CPU 3 are stored in the latch memory 8 via the data bus 30 and drive external loads 26 via output transistors 23. To cope with a large number of control outputs, a plurality of latch memories are used, and the control outputs are stored in the latch memories chip-selected by the CPU 3.
Reference numeral 24 is driving base resistors of the transistors 23, numeral 25 is stable resistors connected between base/emitter terminals of the transistors 23, numeral 27 is an output contact of a feeding power supply relay for the external loads 26.
The conventional apparatus of above arrangement has problems as follows. The LSI 2 becomes large in size because the CPU 3 handles a large number of inputs and outputs. The parallel capacitors 16 acting as a noise filter require capacitors having a variety of capacities to secure a desired filter constant, thereby causing a difficulty in standardization, and it is necessary to employ a large capacitor to secure a large filter constant, increasing the ECU 1 in size.
As a measure for reducing the input/output terminals of the LSI 2 to miniaturize the LSI 2, for example, Japanese Patent Laid-Open (unexamined) No. 13912/1995 specification xe2x80x9cInput/Output Processing ICxe2x80x9d discloses a method of time-sharing and transferring a large number of input/output signals using a serial communication block.
However, this method requires a noise filter of various capacities and is not suitable for standardization of the device. Moreover, a capacitor demands a large capacity to obtain a sufficient filter constant and is not suitable for miniaturization of the device.
Meanwhile, a concept has been publicly known in which a digital filter is used as a noise filter for ON/OFF input signals and the filter constant is controlled by a microprocessor. For example, in xe2x80x9cProgrammable Controllerxe2x80x9d disclosed in Japanese Patent Laid-Open (unexamined) No. 119811/1993 specification, when any input logic value of an external input signal subjected to sampling is successively set at the same value for more than one time, the signal is adopted and stored in an input image memory, and a filter constant changing command is provided for changing a sampling period.
In this method, although a filter constant can be freely changed, a microprocessor bears a large burden in handling a large number of input signals, resulting in slower response of control.
As another example of a digital filter for ON/OFF input signals, Japanese Patent Laid-Open (unexamined) No. 89974/2000 specification discloses xe2x80x9cData Storage Control Circuitxe2x80x9d, in which a shift register is provided as hardware and sampling is carried out according to the same concept as described above.
As described above, however, the mentioned conventional is partially but is not fully miniaturized and standardized in an integral manner. Particularly, in case of miniaturizing and standardizing an input/output circuit of the microprocessor, it is not possible to avoid reduction in original control capability and response of the microprocessor.
In order to solve the above-discussed problems, the first object of the present invention is to provide an on-vehicle electronic controller capable of reducing a burden of a microprocessor in processing input and output to improve its original control capability and response and achieving entire miniaturization and standardization of the controller by reducing an input filter in size.
The second object of the invention is to provide an on-vehicle electronic controller capable of changing a control program and a control constant for various types of vehicle each having different control specifications so as to readily standardize the hardware in a more effective manner.
An on-vehicle electronic controller according to the invention includes a microprocessor having a nonvolatile memory, in which a control program for a controlled vehicle and a control constant are written by an external tool, and a RAM memory for computation. The mentioned on-vehicle electronic controller also includes direct input interface circuits and direct output interface circuits that are connected to a data bus of the mentioned microprocessor and handle high-speed inputs and outputs for engine drive control. The mentioned on-vehicle electronic controller further includes a first serial-parallel converter connected to the mentioned microprocessor via a data bus, a second serial-parallel converter serially connected to the mentioned first serial-parallel converter, and a communication control circuit for serial communication connected to the mentioned second serial-parallel converter via a data bus. The mentioned on-vehicle electronic controller further includes an output latch memory for storing control output signals transmitted via the mentioned first/second serial-parallel converter with respect to low-speed output signals of an auxiliary driving output and an alarm display output, and indirect output interface circuits each connected to an output terminal of the mentioned output latch memory. Furthermore, the mentioned on-vehicle electronic controller includes indirect input interface circuits each having a variable filter circuit provided with constant setting registers in which a filter constant is stored, and to which manually controlled low-speed input signals are inputted. In the mentioned on-vehicle electronic controller, a plurality of ON/OFF information data inputted via the mentioned indirect input interface circuits are serially transmitted to the mentioned RAM memory, and the filter constant of the control constant stored in the mentioned nonvolatile memory is serially transmitted to the mentioned constant setting registers.
In the on-vehicle electronic controller of above constitution, signals inputted via the indirect input interface circuits having the variable filter circuit are serially transmitted to the microprocessor, and the filter constant of the control constant stored in the nonvolatile memory is serially transmitted to the constant setting registers of the mentioned variable filter circuit.
As a result, number of the input/output pins of the microprocessor is largely reduced, and consequently the apparatus becomes small-sized and inexpensive. Furthermore, it is no more necessary to use any large-capacity capacitor of various capacities for the input filter, and consequently the indirect input interface circuit section is effectively miniaturized and standardized.
In particular, because control program and control constant conforming to the type of controlled vehicle are set in the nonvolatile memory in a collective manner, it is now possible to achieve standardization with a high degree of freedom.
It is also possible to lighten the burden of the microprocessor in processing inputs and outputs and improve its original control capability and response.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.